The master's thesis is devoted to the comparison of different types of lithium-ion batteries. Primarily, an introduction to electrochemical power sources and their division is described. Furthermore, the thesis deals only with lithium-ion batteries. In the theoretical part, the chapters discuss the history, the principle of operation and a detailed description of the main battery parts, including used materials. A comparison of commercially available lithium-ion cells with each other as well as with other types of batteries is also included in the theoretical part. The practical part deals with the cyclinf of lithium-ion cells and subsequent evaluation of the effect of temperature on the capacitance and current characteristics of these lithium-ion batteries.

In the early 1970s, research carried out on rechargeable lithium batteries at the Exxon Laboratories in the US established that lithium ions can be intercalated electrochemically into certain layered transition-metal sulphides, the most promising being titanium disulphide. Stemming from this discovery for titanium disulphide, there has been increased interest on lithium-ion intercalation compounds for application in rechargeable batteries. The first rechargeable lithium cell was commercialized in late 1980s by Moli Energy Corporation in Canada. The cell comprised a spirally wound lithium foil as the anode, a separator and MoS2 as the cathode. The cell had a nominal voltage of 1.8 V and an attractive value of specific energy, which was 2 to 3 times greater than either lead-acid or nickel-cadmium cells. However, the battery was withdrawn from the market after safety problems were experienced. This paved way for the discovery of lithium-ion battery. The origin of lithium-ion battery lies in the discovery that Li+-ions can be reversibly intercalated within or deintercalated from the van der Walls gap between graphene sheets of carbon materials at a potential close to the Li/Li+ electrode. Thus, lithium metal is replaced by carbon as the anode material for rechargeable lithium-ion batteries, and the problems associated with metallic lithium mitigated. Complimentary investigations on intercalation compounds based on transition metals resulted in establishing LiCoO2 and LiNiO2 as promising cathode materials. By employing aforesaid intercalation materials, namely carbon and LiCoO2 respectively, as negative and positive electrodes in a non-aqueous lithium-salt electrolyte, a Li-ion cell with a voltage value of about 3.5 V resulted. These findings led to a novel rechargeable battery technology. Lithium-ion batteries were first introduced commercially in 1991 by the Sony Corporation in Japan. Other Japanese manufacturers soon entered the market, followed closely by American and European companies. The subsequent growth in sales of the batteries was truly phenomenal. Beginning from 1991, the lithium-ion battery market has grown from an R&D interest to sales of over 400 million units in 1999. The global market value for lithium-ion batteries at original equipment manufacturer level was estimated to be $1.86 billion in 2000. By 2006, the market is expected to grow to over 1.2 billion units with value of over $4 billion, while the average unit price is expected to fall. Initially, realizable specific energy of commercial Li-ion battery was only about 120 Wh kg-1. However, with continuing improvements in various cell components, present day Li-ion batteries can provide a specific energy density of about 200 Wh kg-1. With the ‘holy grail’ far to be realized, the current R&D efforts are focussed on furthering the specific energy of lithium-ion batteries in conjunction with safety, environmental compatibility, and cost effectiveness. In the Li-ion cell, all of its electrochemical constituents, namely anode, cathode and electrolyte are central to its performance. This thesis describes some novel studies on cathode and anode materials for lithium-ion Batteries.

The increasing demand for electric vehicles (EVs) has led to technological advancementsin the field of battery technology. State of charge (SOC) estimation is a vital function ofthe battery management system - the heart of EVs, and Kalman filtering is a commonmethod for SOC estimation. Due to the non uniformities in tuning and testing scenarios,quantifying performance of SOC estimation algorithms is difficult. Gathering data fordifferent operational scenarios is also cumbersome. In this thesis, SOC estimation algorithmsare developed and tested for a variety of scenarios like varying sensor noise andbias properties, varying state and parameter initializations as well as different initial celltemperatures. A validated and open-source simulation plant model is used to enable easygathering of data for different operational scenarios.The simulation results show that unscented Kalman filter performs better than extendedKalman filter in presence of hard nonlinearities and high initial uncertainties. However,both filters gave similar performance under nominal conditions implying that the choiceof estimation algorithms must depend on operational scenarios. Observability analysisalso gave valuable information to aid in selection of algorithms. The simulation plantmodel facilitated easy data collection for initial development of algorithms, which werethen tested successfully using a real dataset. Further testing using real datasets is requiredto enhance validation. / Den ¨okande efterfr°agan p°a elfordon har lett till teknologiska framsteg inom omr°adet batteriteknik.Estimering av batteriets laddningstillst°and ¨ar en essentiell funktion i batteristyrsystemet,hj¨artat i ett elfordon, och g¨ors ofta genom att till¨ampa metoden Kalmanfiltrering.P°a grund av varierande implementations och testmetodik i litteraturen ¨ar detsv°art att kvantifiera estimeringsalgoritmer. I denna avhandling utvecklas algoritmer f¨oratt estimera ett batteris laddningstillst°and. Algoritmerna testas f¨or olika former av sensorfeloch initialtillst°and, samt f¨or en rad olika temperaturer. En validerad datormodell avbatteri, sensorer och omgivning nyttjas f¨or att generera representativa data f¨or de olikaf¨orh°allandena.Simuleringsresultat visar att den s°a kallade doftl¨osa varianten av Kalmanfiltret (UKF)presterade b¨attre ¨an det utvidgade Kalmanfiltret (EKF) i fall d¨ar systembeteendet ¨ar mycketolinj¨art och d°a initialtillst°andet ¨ar os¨akert. Under normala f¨orh°allanden presterardock de b°ada algoritmerna likv¨ardigt, vilket antyder att valet av algoritm b¨or g¨oras medavseende anv¨andningsscenario. En observerbarhetsanalys av de olika filtervarianterna gavytterligare v¨ardefull information f¨or valet av algoritm. Efter utveckling av filtreringsalgoritmernai simuleringsmilj¨o utf¨ordes tester p°a faktiska m¨atdata med goda resultat. F¨or attfullst¨andig validering av algoritmerna kr¨avs emellertid mer utt¨ommande tester.

In recent years, the demand for Li-ion-type batteries has been increasing significantly in various fields of applications including portable electronics, electric vehicles, and also in renewable energy support. These applications ask for a highly efficient charging strategy in order to maintain a long life cycle of the batteries. Recently, a new charging technique referred as sinusoidal ripple current-constant voltage charging (SRC-CV) technique has been proposed and is in certain publications claimed to realize an improved charging per-formance on Li-ion batteries than conventional constant-current constant-voltage charg-ing (CC-CV) techniques. In this thesis, the charging performance of the SRC-CV charging method applied to a prismatic Li-ion cell for an automotive traction application is inves-tigated. An existing experimental setup is upgraded to realize charging of the Li-ion cells using the SRC-CV charging method. Electrochemical impedance spectrums of three Li-ion cells have been obtained using electrochemical impedance spectroscopy (EIS). These spectrums were used to determine the charging ripple-current frequency where the mag-nitudes of the ac impedance of the cell are minimized. Key parameters like charging time, discharging time, and energy efficiency are calculated in order to compare the charg-ing performance of the CC-CV and SRC-CV charging techniques. The results reported from the experimental results obtained in this thesis indicate that there is no significant improvement with the SRC-CV charging method (implemented using a constant ripple-current frequency) compared to the CC-CV method in terms of charging time and energy efficiency. / På senare tid har behovet av batterier av Li-jontyp ökat kraftigt inom ett flertal applikationsområden inkluderande portabel elektronik, elfordon och miljövänlig elenergiproduktion. I dessa applikationsområden behövs en högeffektiv laddstrategi för att möjliggöra ett stort antal cyklingar av batterierna. Nyligen har en new laddmetod, benämnd sinusoidal ripple current-constant voltage-laddning (SRC-CV-laddning) föreslagits och har i vissa publikationer demonsterat en förbättring av laddprestanda hos Li-jonbatterier jämfört med konventionell constant-current constant-voltage-laddning (CC-CV-laddning). I detta examensarbete undersöks laddprestandan hos SRC-CV och CC-CV-laddning när de appliceras på prismatiska Li-jonceller avsedda för traktionsdrift. En existerande experimentuppsättning har uppgraderats för att realisera laddcykling med SRC-CV-laddning. Med hjälp av elektrokemisk impedansspektroskopi på tre Li-jonceller har den frekvens vid vilken magnituden på cellernas impedans är minimerad identifierats. Nyckelparametrar såsom laddtid, urladdningstid och energieffektivitet har uppmätts för både SRC-CV- och CC-CV-laddning. De experimentella resultaten visar ingen signifikant förbättring mellan SRC-CV-laddning (implementerat med en konstant rippelströmfrekvens) och konventionell CC-CV-laddning.

Lithium-ion battery is attractive for various applications because of its high energy density. The performance of Li-ion battery is influenced by several properties of the electrode materials such as particle size, surface area, ionic and electronic conductivity, etc. Porosity is another important property of the electrode material, which influences the performance. Pores can allow the electrolyte to creep inside the particles and also facilitate volume expansion/contraction arising from intercalation/deintercalation of Li+ ions. Additionally, the rate capability and cycle-life can be enhanced. The following porous electrode materials are investigated. Poorly crystalline porous -MnO2 is synthesized by hydrothermal route from a neutral aqueous solution of KMnO4 at 180 oC and the reaction time of 24 h. On heating, there is a decrease in BET surface area and also a change in morphology from nanopetals to clusters of nanorods. As prepared MnO2 delivers a high discharge specific capacity of 275 mAh g-1 at a specific current of 40 mA g-1 (C/5 rate). Lithium rich manganese oxide (Li2MnO3) is prepared by reverse microemulsion method employing Pluronic acid (P123) as a soft template. It has a well crystalline structure with a broadly distributed mesoporosity but low surface area. However, the sample gains surface area with narrowly distributed mesoporosity and also electrochemical activity after treating in 4 M H2SO4. A discharge capacity of about 160 mAh g-1 is obtained at a discharge current of 30 mA g-1. When the acid-treated sample is heated at 300 °C, the resulting porous sample with a large surface area and dual porosity provides a discharge capacity of 240 mAh g-1 at a discharge current density of 30 mA g-1. Solid solutions of Li2MnO3 and LiMO2 (M=Mn, Ni, Co, Fe and their composites) are more attractive positive electrode materials because of its high capacity >200 mAh g-1.The solid solutions are prepared by microemulsion and polymer template route, which results in porous products. All the solid solution samples exhibit high discharge capacities with high rate capability. Porous flower-like α-Fe2O3 nanostructures is synthesized by ethylene glycol mediated iron alkoxide as an intermediate and heated at different temperatures from 300 to 700 oC. The α-Fe2O3 samples possess porosity with high surface area and deliver discharge capacity values of 1063, 1168, 1183, 1152 and 968 mAh g-1 at a specific current of 50 mA g-1 when prepared at 300, 400, 500, 600 and 700 oC, respectively. Partially exfoliated and reduced graphene oxide (PE-RGO) is prepared by thermal exfoliation of graphite oxide (GO) under normal air atmosphere at 200-500 oC. Discharge capacity values of 771, 832, 1074 and 823 mAh g -1 are obtained with current density of 30 mA g-1 at 1st cycle for PE-RGO samples prepared at 200, 300, 400 and 500 oC, respectively. The electrochemical performance improves on increasing of exfoliation temperature, which is attributed to an increase in surface area. The high rate capability is attributed to porous nature of the material. Results of these studies are presented and discussed in the thesis.